Miniature telephoto lens assembly
An optical lens assembly includes five lens elements and provides a TTL/EFL<1.0. In an embodiment, the focal length of the first lens element f1<TTL/2, an air gap between first and second lens elements is smaller than half the second lens element thickness, an air gap between the third and fourth lens elements is greater than TTL/5 and an air gap between the fourth and fifth lens elements is smaller than about 1.5 times the fifth lens element thickness. All lens elements may be aspheric.
1. A lens assembly, comprising: a plurality of lens elements arranged along an optical axis and spaced apart by respective spaces, wherein the lens assembly has an effective focal length (EFL), a total track length (TTL) of 6.5 millimeters or less and a ratio TTL/EFL<1.0, wherein the plurality of lens elements includes, in order from an object side to an image side, a first group comprising lens elements L 1 _ 1 , L 1 _ 2 and L 1 _ 3 with respective focal lengths f 1 _ 1 , f 1 _ 2 and f 1 _ 3 and a second group comprising lens elements L 2 _ 1 and L 2 _ 2 , wherein the first and second groups of lens elements are separated by a gap that is larger than twice any other gap between lens elements, wherein lens element L 1 _ 1 has positive refractive power and lens element L 1 _ 2 has negative refractive power and wherein lens elements L 2 _ 1 and L 2 _ 2 have opposite refractive powers.
2. The lens assembly of claim 1 , wherein the TTL is equal or smaller than 6.0 mm and wherein the lens assembly has a f-number F#<2.9.
3. The lens assembly of claim 1 , wherein the TTL is equal or smaller than 6.0 mm and wherein lens element L 1 _ 1 has an image-side surface diameter between 2.3 mm and 2.5 mm.
4. The lens assembly of claim 1 , wherein f 1 _ 1 <TTL/2.
5. The lens assembly of claim 1 , wherein the lens assembly has a f-number F#<2.9.
6. The lens assembly of claim 5 , wherein lens element L 1 _ 1 has a concave image-side surface.
7. The lens assembly of claim 1 , wherein the lens assembly has a f-number F#=2.
8. The lens assembly of claim 5 , wherein lens element L 1 _ 1 has a convex image-side surface.
9. The lens assembly of claim 1 , wherein 1.2×|f 1 _ 3 |>1.5×f 1 _ 1 .
10. The lens assembly of claim 1 , wherein 1.2×|f 1 _ 3 |>|f 1 _ 2 |>1.5×f 1 _ 1 .
11. The lens assembly of claim 1 , wherein a combined power of lens elements L 1 _ 2 and L 1 _ 3 is negative.
12. The lens assembly of claim 1 , wherein L 1 _ 3 has negative refractive power.
13. The lens assembly of claim 1 , wherein the gap between lens elements L 2 _ 1 and L 2 _ 2 is smaller than 1.5×d 2 _ 2 , where d 2 _ 2 is a thickness of lens element L 2 _ 2 along the optical axis.
14. The lens assembly of claim 1 , wherein lens elements L 2 _ 1 and L 2 _ 2 are separated by a gap smaller than TTL/20.
15. The lens assembly of claim 1 , wherein L 2 _ 1 and L 2 _ 2 are made of different lens materials having different Abbe numbers, such that one lens element has Abbe number that is smaller than 30 and the other lens element has an Abbe number that is larger than 50.
16. The lens assembly of claim 2 , wherein the lens assembly further includes a ratio between a largest optical axis thickness L 11 and a circumferential edge thickness Lle of lens element L 11 of L 11 /L 1 e <3.
17. A lens assembly, comprising a plurality of lens elements arranged along an optical axis and spaced apart by respective spaces, wherein the lens assembly has an effective focal length (EFL), wherein a lens system that includes the lens assembly plus a window positioned between the plurality of lens elements and an image plane has a total track length (TTL) of 6.5 millimeters or less, wherein a ratio TTL/EFL <1.0, wherein the plurality of lens elements includes, in order from an object side to an image side, a first group comprising lens elements L 1 _ 1 , L 1 _ 2 and L 1 _ 3 with respective focal lengths f 1 _ 2 and f 1 _ 3 , and a second group comprising lens elements L 2 _ 1 and L 2 _ 2 , wherein lens element L 1 _ 1 has positive refractive power and lens element L 1 _ 2 has negative refractive power, wherein 1.2×|f 1 _ 3 |>|f 1 _ 2 |>1.5×f 1 _ 1 and wherein lens elements L 2 _ 1 and L 2 _ 2 have opposite refractive powers.
18. The lens assembly of claim 17 , wherein the TTL is equal or smaller than 6.0 mm and wherein the lens assembly has a f-number F#<2.9.
19. The lens assembly of claim 17 , wherein the TTL is equal or smaller than 6.0 mm and wherein lens element L 1 _ 1 has an image-side surface diameter between 2.3 mm and 2.5 mm.
20. The lens assembly of claim 17 , wherein f 1 _ 1 <TTL/2.
21. The lens assembly of claim 17 , wherein the lens assembly has a f-number F#<2.9.
22. The lens assembly of claim 21 , wherein lens element L 1 _ 1 has a concave image-side surface.
23. The lens assembly of claim 17 , wherein the lens assembly has a f-number F#=2.8.
24. The lens assembly of claim 21 , wherein lens element L 1 _ 1 has a convex image-side surface.
25. The lens assembly of claim 17 , wherein a combined power of lens elements L 1 _ 2 and L 1 _ 3 is negative.
26. The lens assembly of claim 17 , wherein L 1 _ 3 has negative refractive power.
27. The lens assembly of claim 17 , wherein a gap between lens elements L 2 _ 1 and L 2 _ 2 is smaller than 1.5×d 5 , where d 5 is a thickness of lens element L 2 _ 2 along the optical axis.
28. The lens assembly of claim 17 , wherein lens elements L 2 _ 1 and L 2 _ 2 , are separated by a gap smaller than TTL/20.
29. The lens assembly of claim 17 , wherein L 2 _ 1 and L 2 _ 2 are made of different lens materials having different Abbe numbers, such that one lens element has an Abbe number that is smaller than 30 and the other lens element has an Abbe number that is larger than 50.
30. The lens assembly of claim 18 , wherein the lens assembly further includes a ratio between a largest optical axis thickness L 11 and a circumferential edge thickness L 1 e of lens element L 1 _ 1 of L 11 /L 1 e <3.